The present invention relates to a method of connecting two printed wiring boards with each other through an electrical connection of respective electrode patterns formed by electrodes that are disposed in high density, and to a printed circuit board provided by the connection between these printed wiring boards based on this connection method. Particularly, this invention relates to a method of connecting the printed wiring boards with each other that is capable of easily and precisely positioning the electrode patterns and is also capable of fixing the electrode patterns after the positioning, and to the printed circuit board provided by this connection.
In recent years, there has been an increasing market demand for thinner and smaller sizes of semiconductor devices as represented by CPUs and memory ICs that are mounted on an electronic apparatus. Various efforts have been made to meet such demand for smaller sizes and higher functions. In realizing the smaller sizes and higher functions, the CPUs and memory ICs have a large number of electrodes (lead frames) disposed on the periphery of the packages to have electrical connections with external units like semiconductor devices/elements in order to perform signal transmission/reception between them.
Inside the packages of the CPUs and ICs, there are going on connections between chips that function as cores and the large number of lead frames at high speed and in high precision by solder bumper or wire bonding, as a part of the process of manufacturing semiconductors. Further, at the outside of the packages, there are normally mounted as functional modules a large number of CPUs, memory ICs and semiconductors in high precision on one printed circuit board. As they are located at mutually close positions, their lead frames are also electrically connected with no problem on the printed circuit board to form high-precision and high-density wiring patterns.
In the mean time, in the technical field of display units that function as output interfaces with users, there have been developed matrix-display type display units such as liquid displays and plasma displays for realizing thin types and lower power consumption in place of the conventional CRT displays. In recent years, the needs for higher resolution and larger screens of these displays have been increasing. In order to meet the needs, various developments have also been progressed.
In such a matrix-display type display unit, a display panel composed of a plurality of pixel elements is usually formed separately from a control unit that controls the display of images. Particularly, on each display panel, there are laid out a large number of electrodes to achieve signal transnission/reception to/from the control unit, corresponding to the number of pixel elements that make displays. Therefore, in order to achieve the above-described higher resolution and larger screens, it is necessary to provide a larger number of electrodes (hereinafter to be referred to as an electrode pattern).
However, this electrode pattern is required to be integrated in compact as far as possible in consideration of a limited area of the display panel and easiness of connecting the display panel with the control unit. Accordingly, it becomes necessary to reduce a distance between adjacent electrodes that structure the electrode pattern. In other words, it is necessary to narrow the pitch of the electrode pattern.
Further, other types of electronic apparatus may also be constructed to have a plurality of printed circuit boards that have the narrow-pitched electrode patterns. In many cases, functions to be achieved by the printed circuit boards are provided in the form of modules on each printed circuit board. In the actual transactions, in many cases, these printed circuit boards are supplied by different makers.
Therefore, for achieving electrical connection of the electrode patterns between the printed circuit boards that have the narrow-pitched electrode patterns, there are usually used printed wiring boards such as FPCs (flexible printed circuits). There is also a case where the printed circuit boards are directly connected with each other by using a connector. Therefore, in order to connect a printed circuit board with a printed wiring board, or to connect printed circuit boards with each other, there has been required a method that can achieve an easy and precise positioning of mutually narrow-pitched electrode patterns.
In the following description of connection methods, there will be no distinction between the connection between a printed circuit board and a printed wiring board and the connection between two printed circuit boards. The description will be made based on the connection between printed wiring boards.
FIG. 1A to FIG. 1C explain a conventional method of connecting a printed wiring board with another printed wiring board. Particularly, these figures show an example of connecting a plasma display panel with an FPC. As shown in these figures, for connecting the printed wiring board with the FPC, each having a high-density electrode pattern, the electrode patterns are directly positioned based on visual observation. The printed wiring boards connected are then fixed.
The connection is carried out as follows. First, a tape 215 is adhered in advance onto the surface of an electrode pattern 213 of an FPC 210 as shown in FIG. 1A. Based on a visual observation, an electrode pattern 203 of a printed wiring board 200 and an electrode pattern 213 of the FPC 210 are positioned together to achieve a mutual electrical connection.
The tape 215 provisionally fixes the printed wiring board 200. A pressing metal member 220 is then applied to the electrode pattern 213 of the FPC 210, as shown in FIG. 1B. Spring clips 230 are applied to sandwich the pressing metal member 220, the printed wiring board 200 and the FPC 210 together, as shown in FIG. 1C. Thus, the printed wiring board 200, the FPC 210 and the pressing metal member 220 are fixed integrally.
In this way, the electrode pattern 203 of the printed wiring board 200 and the electrode pattern 213 of the FPC 210 are electrically connected and fixed together.
As another conventional method of connecting between printed wiring boards, there is disclosed xe2x80x9cA method of positioning a printed wiring board and partsxe2x80x9d in Japanese Patent Application Laid-open No. 8-37397. According to this method, a positioning pattern is formed on a printed wiring board, and a solder is adhered to this positioning pattern to form projections. These projections are then engaged with holes provided on parts that are to be positioned (electric parts and other printed wiring board or the like). Thus, the parts are disposed on the printed wiring board.
Based on the above method, it is not necessary to prepare a tool equipped with positioning pins that have been conventionally required. It is not necessary to form positioning holes on the printed wiring board either. As compared with the conventional methods of positioning a printed wiring board and parts, this method can improve the precision of the positioning.
However, according to the above conventional methods of connecting between printed wiring boards, there is no reference of positioning other than electrode patterns. Therefore, it has been necessary to directly position narrow-pitched electrode patterns based on a visual observation. As a result, there have frequently occurred positional deviations between the electrode patterns. Thus it has been necessary to carefully confirm the connection between the printed wiring boards after the fixing by the clips 230.
Further, in fixing between the printed wiring boards after the positioning, it is necessary to use a plurality of independent parts such as the pressing metal member 220 and the spring clips 230. This makes the fixing work complex, and also requires many fitting processes, which has lowered the productivity.
The above xe2x80x9cA method of positioning a printed wiring board and partsxe2x80x9d is a method of positioning based on the formation of a plurality of projections by solder and the holes of the parts. As the holes of the parts are usually formed mechanically, in many cases the tolerance becomes larger than the pitches of the high-density electrode patterns. As a result, after the printed wiring board and the parts have been positioned, the precision of the positioning between the respective electrode patterns is lowered. Thus, it has been difficult to achieve a precise positioning.
It is an object of the present invention to facilitate a precise positioning between printed wiring boards that have narrow-pitched electrode patterns respectively, and to facilitate a secure fixing of the connected printed wiring boards after the positioning.
In order to achieve the above object by solving the above problems, according to one aspect of the present invention, there are provided a method of connecting between printed wiring boards, and a printed circuit board having printed wiring boards connected based on this connection method, as follows. This method has a process of forming at one end of a first printed wiring board a first electrode pattern together with first engagement patterns made of the same material as that of the first electrode pattern near this first electrode pattern; and a process of forming at one end of a second printed wiring board a second electrode pattern together with second engagement patterns made of the same material as that of the second electrode pattern near this second electrode pattern, the second engagement patterns being engageable with the first engagement patterns. Therefore, it is possible to easily obtain engagement patterns having high-precision shapes without separately providing a new process.
According to the above invention, when the first engagement patterns are engaged with the second engagement patterns, it is possible to position the electrode patterns so that the first electrode pattern is electrically connected with the second electrode pattern.
According to another aspect of the invention, there are provided a method of connecting between printed wiring boards, and a printed circuit board having printed wiring boards connected based on this connection method, as follows. This method has a process of forming first engagement patterns by plating on a part of a first electrode pattern at one end of a first printed wiring board; and a process of forming second engagement patterns by plating on a part of a second electrode pattern at one end of a second printed wiring board.
According to the above invention, when the first engagement patterns are engaged with the second engagement patterns, it is possible to position the electrode patterns so that the first electrode pattern is electrically connected with the second electrode pattern.
According to still another aspect of the invention, there are provided a method of connecting between printed wiring boards, and a printed circuit board having printed wiring boards connected based on this connection method, as follows. This method has a process of forming at one end of the first printed wiring board a covering material that covers an upper surface of a first printed wiring board other than a portion of the upper surface where a first electrode pattern is electrically connected so that one end of the covering material positioned at the first electrode pattern side has a first rugged part in a direction parallel with the surface of the first printed wiring board; and a process of forming a covering material that covers an upper surface of a second printed wiring board other than a portion of the upper surface where a second electrode pattern is electrically connected at one end of the second printed wiring board so that one end of the covering material positioned at the second electrode pattern side has a second rugged part in a direction parallel with the surface of the second printed wiring board.
According to the above invention, when the first rugged part is engaged with the second rugged part, it is possible to position the electrode patterns so that the first electrode pattern is electrically connected with the second electrode pattern.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.